The specific aim of this research is to study the anatomical connections and organization of the basal ganglia and related nuclei in the monkey using retrograde and anterograde axonal transport techniques. Studies will be directed towards determining: (1) the afferent and efferent projections of the substantia nigra, (2) the afferent and efferent projections of the subthalamic nucleus, and (3) the origin, terminations and relationships of pallidofugal fiber systems to their relay nuclei. The afferent projections of the subthalamic nucleus and the substantia nigra will be determined by injecting horseradish peroxidase (HRP) into these nuclei and studying neurons to which this enzyme is transported in retrograde fashion. Pallidofugal fiber systems will be investigated by injecting HRP into thalamic relay nuclei (ventral anterior, VApc; ventral lateral, Vlo and the centromedian, CM) and into portions of the midbrain reticular formation (i.e., the pedunculopontine nucleus). Studies of the retrograde transport of HRP should provide data concerning the precise locations of pallidal neurons which project fibers to these loci. It is proposed to determine the efferent projections of the subthalamic nucleus, substantia nigra, globus pallidus and the pedunculopontine nucleus by injecting small volumes of tritiated amino acids into these nuclei. Studies of the anterograde axonal transport of labeled materials will be made from serial autoradiographs. Serial autoradiographs will be studied in bright and dark field illumination and maps will be made of the locations of the developed silver grains over axonal terminals. It is apparent that anatomical data based largely upon degeneration studies are incomplete. The object of this study is to elucidate the functional significance of individual components of the basal ganglia and how they make their contributions to motor function.